[IIAOPSW]

Wow. This is exactly like a speculative comment I was going to write. Only thing I'll add is the relation seems to hold for other animals. The bigger the animal, the longer the wavelengths in both vocalizations and (to the limited extent we can study), brain waves. Think about the reaction times of a whale vs the reaction times of a small bird. I bet videos of whales speed up kind of look like videos of birds.